Lymph flow and lung water both increase in pulmonary edema before the stage of alveolar flooding and the development of the clinical syndrome. The sequence of the early changes in lung edema needs clarification. Our objective is to better delineate the sequence of early changes in lung edema and clarify the relation between changes in lung interstitial water, pulmonary capillary blood volume and lymph flow from the lung. A rebreathing technique for the determination of pulmonary parenchymal tissue volume (Vt), pulmonary capillary blood volume (Vc), cardiac output (Qc), and membrane diffusing capacity (DM) will be applied to sheep and calves prepared with lung lymph fistulae. Left atrial pressure will be regulated by mitral orifice balloons, by left ventricular to left atrial shunting in left ventricular transapical bypass preparations (LVTAB) or by differential regulation of right and ventricular outputs in pneumatically controlled total artificial heart (TAH) preparations. Animals prepared with LVTAB or TAH will serve as models of chronic heart failure.